a) this is an exothermic process as liquid water is cooled to convert into ice (solid state). b) this is an endothermic reaction as formation of water from hydrogen and oxygen involves more energy to break the bonds to form new ones. c) this involves cooling of water, and that is an exothermic process. d) this involves breaking of hydrogen bonding between water molecules which requires energy, so it is an endothermic process.
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As given in answer